Protective circuit arrangements have been provided in the past to protect electrical devices such as electrical appliances and personnel or users of the devices when undesirable conditions develop within the device. Examples of such arrangements are set forth in the applicant's prior U.S. Pat. No. 6,525,914—Protection System for Devices Connected to an Alternating Current Electrical Power Supply, and U.S. Pat. No. 6,829,123—Device Safety System and Method. While the systems set forth in these patents offer various levels and types of protection for electrical devices, they are, because of the number and type of electrical components involved, and assemble costs, quite expensive when considered as a part of the overall cost of the device in which they are provided for protection. Unfortunately the technology described in those documents was never incorporated into consumer appliances because the manufacturers that were contacted considered that the added cost would be inappropriate for market acceptance.
Manufacturers of electrical appliances are continually trying to reduce the cost of manufacturing the appliances. As the cost of manufacturing the appliance decreases, the relative cost of protective circuit arrangements such as those set forth in the above-mentioned patents becomes much greater, such that the manufacture becomes more reluctant to include them in the appliance. Rather than not include protective arrangements in an appliance, it is desirable to provide protection in a relatively less costly way. The need exists for a protective circuit configuration that addresses consumer safety issues to be available at a cost that could more readily be acceptable to this highly competitive industry, and thus would encourage appliance manufacturers to include it in their products.
While electrical appliances are designed to be reliable and safe to use, unsafe conditions can develop such as due to a failure in a component of the appliance, or due to miss-use of the appliance. For instance, an electrical toaster may present the following unsafe conditions. The elevator carriage may become jammed in the down position, thereby keeping the electrical heating elements activated. Excessive leakage currents from metal parts to electrically live parts such as the elements, may develop, such as caused by a build up of crumbs and grease between the metal parts and electrically live parts. Fire or flames developing within the toaster. A contact being made between the metal frame and electrically live parts by person sticking a metal object, such as a knife into the toaster. It is therefore desirability to include automatic protective features in certain consumer appliances that will contribute to both the protection of property and consumer safety.
In an October 2012 press release, the Consumer Product Safety Commission (CPSC) states that approximately 40% of the residential fires each year are caused by cooking equipment. Additionally, the National Fire Protections Association (NFPA) statistics indicate that 23% of these fires involve ovens or rotisseries, microwave ovens, and toaster/toaster ovens.
Another well known undesirable electrical hazard associated with consumer kitchen appliances such as toasters and toaster ovens is dangerous leakage current which can cause fires resulting in property damage, serious injury from electrical shock or result in electrocutions. Excessive electrical leakage current may occur between accessible metal part and electrically live parts due to contributing situations such as: insulation damage or failure, build up of conductive substances, and insertion of foreign bodies etc. all of which create hazardous conditions.
Fire is also a major safety issue for electrical appliances especially those containing heating elements. Toasters and toaster ovens for example, have a documented history of extremely hazardous fire related events that have and can lead to property destruction and deaths. If such a hazardous fire event occurs it is important to limit the time duration of the fire by removing the power source and if possible to contain the fire in the appliance compartment. For toasters having elevator carriages, it is necessary to maintain the carriage in the down position, so as to avoid it springing up and spreading flaming debris in the area around the toaster. An audible or visual alarm is desirable to bring attention to a hazardous condition.
Protecting the user and an appliance by removing electrical power is essential, for instance, when a consumer inserts a conductive implement into a typical toaster compartment that contains metal supports for the bread or bagel. Protection would be provided, since it would be extremely unlikely for the conductive implement to make contact with the electrically live heating element without also making contact with the metal supports. Protection is also desirable when combustible or conductive material enter the toaster compartment. Protection is also desirable in the case of insulation damage, and when a broken or damaged live electrical element makes contact with a metal case of the appliance.